Topological multiferroic order in twisted transition metal dichalcogenide bilayers

TL;DR

This paper predicts a topological multiferroic state in twisted transition metal dichalcogenide bilayers, combining magnetic, electric, and topological properties, tunable via external fields and substrate effects.

Contribution

It introduces a novel topological multiferroic order in twisted bilayers, linking Coulomb interactions, spin-orbit coupling, and topological electronic states in van der Waals materials.

Findings

Emergence of ferrimagnetic and ferroelectric orders at quarter-filling.

Presence of a non-zero Chern number indicating topological order.

Interface modes tunable by electric fields and substrate-induced supermoire effects.

Abstract

Layered van der Waals materials have risen as powerful platforms to artificially engineer correlated states of matter. Here we show the emergence of a multiferroic order in a twisted dichalcogenide bilayer superlattice at quarter-filling. We show that the competition between Coulomb interactions leads to the simultaneous emergence of ferrimagnetic and ferroelectric orders. We derive the magnetoelectric coupling for this system, which leads to a direct strong coupling between the charge and spin orders. We show that, due to intrinsic spin-orbit coupling effects, the electronic structure shows a non-zero Chern number, thus displaying a topological multiferroic order. We show that this topological state gives rise to interface modes at the different magnetic and ferroelectric domains of the multiferroic. We demonstrate that these topological modes can be tuned with external electric fields as well as triggered by supermoire effects generated by a substrate. Our results put forward twisted van der Waals materials as a potential platform to explore multiferroic symmetry breaking orders and, ultimately, controllable topological excitations in magnetoelectric domains.